Distributed Control Systems (DCS) have been employed in process plants for controlling plant processes in the process plant. A DCS can have controllers that are embedded devices. A controller for a DCS can also be a general or Industrial Computer, Programming Logic Controller (PLC), and any computing unit capable of providing a real time execution environment to control applications.
It will be understood that control of processes is essential for proper functioning or operation of a process plant. The processes referenced here are characterized by factors relating to process plant unit operation, associated hardware, control applications, workflow etc. Any change in these factors, such as the control applications, can influence the operation of the process plant. These factors are also constrained by one or more of the system configuration, hardware capability, communication, current state of the process, and by its capabilities thereof, as applicable.
In a distributed control system, the controllers can be distributed and associated with one or more processes/units in a process plant. The process information can be gathered by a controller through an input device connected to a transducer or transmitter, which are field devices, or directly from a field device using compatible protocols. Similarly, a controller output can be used for actuation through an output device or directly through a field device using compatible protocols. It is known to have one or more Input-Output (IO) devices and field devices allocated to a specific controller (e.g., these devices would communicate with only the specific controller connected with them). Therefore, the control applications executing on a controller can have access to a limited and preconfigured set of I/O devices or field devices. Hardware devices called Communication Interface (CI) modules can be used to connect and scale the number of I/O units and field devices which can be allocated to a controller. CI modules can include a master and a slave hardware component where a CI master is attached to a controller while a CI slave is used as a convergence point for several I/O/field devices. Thus, each I/O unit is configured to serve and to be connected to a single controller in a network. For efficient execution of a control application, process information gathered from an I/O unit or from field devices can be as far as possible executed in a single controller. In cases where this is not possible, process information can be shared using a controller to controller communication, thus providing indirect access of process information to another controller to execute associated control applications.
The configuration of a DCS can be static; e.g., they do not generally allow direct access to I/O units, dynamic sharing or migration of control applications, or parts thereof (henceforth, parts thereof are said to be included in the reference to a control application), among peer controllers in a plant. However, in practical situations, a control system may adopt or encounter changes or modifications in its configuration with regard to one or more of the factors mentioned herein, during operation. For example, changes to control applications can become significant such that they need to be addressed online (e.g., during the operation of the plant without stopping or suspending the plant operation to have the desired change be incorporated without disturbing the plant operation).
GB 2445636 describes an I/O card that is used to interface two process controllers over a communication line that is separate from a primary communication line connecting the two process controllers to a workstation. The process controllers can access I/O cards in the same manner as I/O cards connect to field devices. Inter-controller communications can be programmed as general I/O communication that may utilize, for example, Ethernet, Token ring, FDDI, ARCNET, WiFi, serial or parallel communication protocols.
It would be desirable to provide a flexible configuration of a DCS that supports dynamic reconfiguration and has a means to provide direct access of process information to peer controllers in the DCS. It would also be desirable to provide a solution that connects information from I/O and field devices to their respective control applications in a situation that involves dynamic distribution of control applications in real time without disturbing the operation of the plant.